Art of springmaking



April 10, 1951 MELETT] 2,548,735

ART OF SPRING MAKING Filed Oct. 1, 1948 "Hul H 'L-Q 8 |4 O INVENTOR.

- 'ADQLPH MELETTI 9 i @QLM% ll/S ATTORNEY Patented Apr. 10, 1951 UNITED STATES PATENT OFFICE Vacuum Cleaner Corporation of America, Philadelphia, Pa., a corporation of Pennsyl- Vania Application October 1, 1948, Serial No. 52,248

5 Claims.

v v I My invention relates to the art of spring inak ing and particularly to the provision of means for the attachment of a motor spring or power spring to an arbor. V

In accordance with my invention, a substantially cylindrical collar having a permanentset is formed from one or a few coils on an end of a strip of tempered spring steel, preferably without material diminution of the initial hardness, temper and resiliency thereof, without materially impairing the characteristics'in the section of the spring immediately adjacent ,to the collar and without increasing the brittleness of the collar or the adjacent springscti'on.

In the preferred practice of my invention, a strip of hardened, tempered, resilient spring steel, of the relatively high carbon content commonly used in spring making, is bent around a, hot former and is quickly and briefly heated from a substantially cold condition to a temperature suflicient to impart a set to the coil but without materially impairing the spring characteristics of the metal. This momentary heating is preferably effected during the coiling of the collar but may take place 'whilethe strip is positioned for coiling without intervening cooling. The requisite temperature "will vary with the composition of the steel, but for a good grade of high carbon spring steel, hardened 'and'tempered before coiling, the collar coil should be heated to or above baking temperature of say 550 F. but below a hardening temperature of 1250" F., and preferably to a temperature between 900 and 1100 so as to provide adequate set and resiliency without excessive brittleness. The 'tim'e'requi'red for coiling the collar and imparting a set thereto by heating is less than a minute and ordinarily only a few seconds.

The heating of the former and of a strip being coiled thereby to form a collar is preferably effected by the creation of an intense magnetic flux in and around them resulting in hysteresis and eddy currents in the former and strip section forming the coil. Preferably, the former is maintained at, or just below, a dull red heat-before and during the formation of the collar. The magnetic flux inducing the heat in the former is preferably maintained during the coiling of the collar to heat the latter by induction as well as conduction from the former, but, under certain conditions, the inductive heating of the strip section forming the collar may be dispensed with and sufflcient heat imparted to such section by conduction alone. It is, however, important for the production of uniform products to provide 2 for uniform quick and thorough heating 'of'the strip. section forming the collar, and this is best attained by the maintenance of high frequency magnetic flux of predetermined intensity in which a mandrel is rotated to coil'thec'ollar and which flux is maintained constant during and in the intervals between the coiling of successive strips.

The principles of my invention, and the best mode which I have contemplated applying such principles, will more fully appear'fr'om the following description and the accompanying drawings in illustration thereof.

In'the drawings, Fig. 1 is a vertical sectional view of an apparatus embodying my invention and for practicing the method forming a part of my invention; Fig. 2 is a partly diagrammatic top plan view of the apparatus shown in Fig. 1; Fig. 3 is a spring strip having a collar wound thereon in accordance with my invention; Fig. '4 is a power spring which is cold wound from the strip shown in Fig. 3; the spring being shown'as it appears after removal from the winding mandrel and before attachment to a reel arbor; and Fig. 5 shows the spring after attachment to the arbor of a reel (not shown) and partly wound up.

In Figs. 1 and 2 in the drawings, there is illustrated a high frequency inductionma'chihe having a motor-generator set I mounted on afra'me 2 for supplying current to the primary 3 of a variable transformer having a secondary 4 in circuit with a water cooled hollow copper tube 5 forming a loop for creating a high frequency magnetic flux when high frequency electric current is supplied to the loop from the transformer. A base 6 is mounted on brackets 1 attached to the frame 2, and a shaft 8 is journalled in vertically spaced bearings of the base and held against upward movement by a collar 8' pinned to the shaft. The shaft 8 has a bevel gear 8 thereon which meshes with and is rotatable by a bevel gear in fixed to a shaft II which is journalled in a bearing block I2 on the base 6 and may be rotated by a handle'l3 or any suitable source of power.

A vertically reciprocal shaft I4 is spl-ined in and rotated by the shaft 8 and contains a socket l5 for the reception of a mandrel I6 whichmay be locked in the socket by a pin lland contains a slit [8 which extends lengthwise of the mandrel on a secant to the periphery thereof. The shaft I4 is vertically reciprocable by the attachment of a treadle or other suitable mechanism (not shown) to the eye l9 to move the mandrel l6 vertically through a feeder and stripper plate 20 which has a guide 20' along one edge thereof for guiding a strip into the slot I8. The feeder and stripper plate 20 has a pedestal supported on an upward extension of the base 6.

An L-shaped lever 2| is fulcrumed n the feeder and stripper plate 20 and is biased toward the surface of the mandrel by a rod 22 which is pressed by a spring 23 whose tension is controlled by an adjusting screw 24.

When the mandrel I6 is in its uppermost position, the mandrel lies between and is spaced from the legs of the loop 5; the loop preferably lying at an angle of 45 with respect to the axis of the mandrel It.

In the practice of my process, the mandrel I6 is projected above the feeder and stripper plate 20 with its slot l8 aligned with the inner surface of the guide 20'. High frequency electric current is supplied to the loop 5 from the secondary 4 of the transformer and creates an intense magnetic flux into which the iron or steel mandrel l6 projects and acts as a species of core concentrating the flux. The resultant molecular friction of hysteresis, eddy. currents and skin effect causes heating of the mandrel, which may, if desired, be localized nearthe surface and the temperature of the heated mandrel may be accurately controlled and maintained by adjustments of the current flowing through the loop 5.

' When the mandrel is heated to approximately a dull red heat,"say 950 F., a flat strip of spring steel is'fed overthe'feeder and stripper plate 20, along theguide 20', until its front edge is inserted vin the slot H3. The handle 13 is turned to' rotate the mandrel 16 so as to bend a lip B on the strip A and wind the latter one or a few turns around the mandrel so as to form a collar (If. During the winding of the strip it is pressed against the mandrel by the pushrod 22 so that the collar conforms closely to the contour of the mandrel. v

During the coiling of the strip A on the mandrel, it is heated, to or slightly below, a dull red heat, say 950 by conduction of heat from the mandrel and by molecular friction of hysteresis, eddy currents, and skin effect produced in the strip. by the magnetic flux in which it is being rotated. The temperature of the coiled section can be regulated and maintained with accuracy by adjusting. the current flowing through the loop 5.

As soon as a collar C has been formed by coiling the end of'the strip A the mandrel I6 is lowered through the stripper plate until the mandrel clears'the bottom of the collar, which is then removed from the magnetic field.

The collar is allowed to cool, preferably withoutquenching. It is free from scale and may be then slipped axially over a cold, slotted mandrel which is rotated to coil the remainder of the strip into a spring, such as illustrated in Fig. 4, with a notch or hook D at the outer end thereof. Such a spring may be readily slipped over a slotted arbor of a reel, with its lip B in the slot of the arbor and the end of the strip A latched to the drum of the reel.

My invention may be used in connection with the coiling of spring materials of various compositions, such, for instance, as those specified in the standard specifications of the A. S. T. M.

for spring materials, but it is particularly useful in connection with the production of motor springs from the best grades of high carbon spring steel, hardened and tempered, and which is commercially produced in long strips, which may be cut into sections of desired length and fed in a continuous sequence to my improved apparatus.

Springs made in accordance with my invention are free from scale and may be made substantially shorter for the same power than usual since it is unnecessary to partially set any part of the spring length beyond that required for gripping th arbor, and springs made in accordance with my invention may be accurately computed to do the work required. The collar maintains a grip at all times on the arbor to which it is fitted.

My method obviates the customary annealling, lip bending, reheating, winding and quenching which result in many defective springs even when skilled heat treaters are employed. The springs produced in accordance with my invention are of high and uniformquality, and may be produced at a much higher rate than usual,- even when unskilled labor is used. r I

Having described my invention, I claim:

1. A method of forming a, collar on a tempered spring strip which comprises coiling an end of the strip by a hot former without preheating the strip for coiling to a temperature above that at which it is coiled and in a magnetic field of sufficient intensity to' efiect induction' heating of the former and end being wound.

2. A method of forming a collar on a tempered spring strip which comprises coiling an endof the strip by a former having a temperature suf ficient to heat such end to at least a baking tem-' perature during the windingthereof. I

3. Apparatus for forming a collar on a thermotropic strip which comprises a rotatable for mer for coiling and end of said strip and an induction coil forming a magnetic flux in said former.

4. A method of forming a collar on a tempered spring strip which comprises coiling an end of such strip while heating the coiling section from the inside outwardly and from a non treatiri g temperature to at least a baking heat.

5. Apparatus for forming a'collar on a tempered spring strip which comprises a loop, a source of high frequency current connected with said loop creating a magnetic field, a slotted mandrel reciprocable into and from said field, and a stripper for detaching a collar from said mandrel upon the Withdrawal thereof from said field. V ADOLPH MELETTI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Hallstrom et a1 Nov. 6, 1945 

